The invention relates to a process for treating a mixture of substances containing structured constituents and organic matter in accordance with the preamble of claim 1, and a device in particular for carrying out this process.
Such a process is, for example, utilized for treating residual waste matter. In DE 196 48 731 A1 a waste matter treatment method is described, wherein the residual waste matter is treated in a percolator. By such a percolation or extraction, organic constituents, inorganic substances and in a given case water-soluble fatty acids are leached from the waste matter by an extracting or washing agent. The residue is withdrawn from the percolator and, following a subsequent drying, supplied to combustion or dumped.
It was found that by this process the organic substances cannot be removed in the required extent from the residual waste matter.
The drawbacks of this known waste matter treatment process may be eliminated by the process for treating biological waste as disclosed in WO 97/27158 A1. In this process a novel percolator is employed wherein the waste matter passes through the reactor in a horizontal direction (longitudinal direction), and a biogenic reaction is superseded to the percolation process by supplying atmospheric oxygen (process air).
As a result of supplying process air, the cells of the organic matter are split open and the liberated organic substances are carried off by the leaching fluid. In order to avoid channel formation within the waste matter and introduce shear forces, an agitator or circulating apparatus is provided in the reactor, whereby the waste matter is mixed thoroughly in a vertical direction (in parallel with the direction of flow of leaching fluid and process air) and also displaced in the direction of transport.
It is a drawback in this process that for guiding and mixing the waste matter within the reactor, a considerable expense must be incurred which substantially influences the investment costs. Such a complex mechanical structure also harbors the risk of failure of the installation owing to a malfunction in the transport system of the reactor, so that a comparatively high expense for servicing the reactor must be incurred. Such downtimes of the reactor as a result of the necessary maintenance or of a malfunction in the reactor periphery may, however, only be neutralized by providing corresponding buffer spaces wherein intermediate storage of the waste matter during the downtime of the reactor is, possible. In DE 196 08 586 A1 a rotting process is described wherein the exposed pit is subjected to pressured air.
In contrast, the invention is based on the object of furnishing a process for treating a mixture of substances containing structured constituents and organic matter, and a device wherein sufficient decomposition of the organic proportion takes place at minimum expense in terms of device technology.
This object is achieved by the features of claim 1 as far as the process is concerned, and by the features of claim 12 as far as the device is concerned.
Through the measures of causing the mixture of substances (for example residual waste matter) containing structured constituents and organic matter to pass through the reactor in the absence of any substantial longitudinal and transversal mixing, and of preventing channel formation by applying forces to the mixture of substances which are directed approximately in parallel with or transversally to the direction of displacement, the reactor may have a substantially more simple construction than in the above described prior art because it is not necessary to provide an agitator for lateral mixing. The forces are preferably introduced from the peripheral area of the reactor, for example through a suitably designed discharge means or by means of injected gas, preferably pressurized air. In particular when pressurized air is used, shear forces are also applied to the bulk material, whereby the surface of the heap material is reorganized and particles of the mixture of substances are separated into fibers.
The reactor nay be employed as a percolator and dryer without any restructuring or modifications becoming necessary.
Upon introduction of the forces preventing channel formation by way of the discharge means, the mixture of substances is preferably circulated at least in part, so that shear forces are introduced due to the conveyor elements bringing about the circulation.
The flow management according to the invention makes it possible to design the reactor with a high degree of compactness, wherein it is possible to position all of the feeding and discharging means at the head or bottom portion of the reactor.
In a particularly preferred embodiment, the forces for prevention of channel formation and the shear forces required for surface reformation and for tearing open the particles are applied through a pressure gas, preferably pressurized air, which is injected into the bulk material (heap material) from the peripheral area of the reactor. By the pressurized air the heap material is partially expanded, so that a surface reformation takes place in the bulk material and the particles are to=open as a result of the introduced shear forcesxe2x80x94the mass transfer area for decomposition of the mixture of substances by means of the atmospheric oxygen and of the leaching fluid is increased.
In a particularly preferred embodiment, the pressurized air and the process air are supplied through nozzles arranged in the foot portion and/or in the bottom portion of the reactor.
In accordance with the invention it is preferred if the mixture of substances passes through the reactor essentially vertically (in parallel with the direction of gravity) or horizontally, so that the mixture of substances is guided approximately in parallel or in a flow transversal to the process air.
In a case where the reactor is employed as a percolator, the leaching fluid is preferably supplied through a distributor in the head portion of the reactor.
The pressurized air is supplied at a pressure of more than 2 bar, preferably more than 4 bar, whereas a pressure of 0.5 bar is customarily applied to the process air.
The nozzles for introduction of the process air and/or pressurized:air may advantageously be controlled individually, so that a specific pressurized air profile may be adjusted across the reactor cross-section.
The use of pressurized air for introducing shear forces and for preventing channel formation has the advantage of the atmospheric oxygen required in the bulk material for the aerobic process being supplied concurrently, so that the pressurized air basically fulfills a twofold function:
1. supplying atmospheric oxygen for aerobic decomposition, and
2. introduction of shear forces.
In a more simple embodiment the forces for preventing channel formation in the bulk material are, for example, supplied through a discharge means arranged at the bottom portion of the reactor. This discharge means may, for example, be a scraper floor installation or a similar conveyor means for discharging the mixture of substances by layers. This variant has the additional advantage of feeding and discharging openings in the bottom portion of the reactor being kept free owing to the advance movement of the discharge means, so that the leaching fluid may exit and pressurized air or process air, respectively, may penetrate into the bulk material. As a discharge means, a worm conveyor carpet, a walking floor, silo filler means etc. may also be used. These discharge means may, of course, also be used in the above described embodiment with pressurized air.
Inasmuch as the mixture of substances passes through the reactor preferably in the form of layers, the dwell time of the mixture of substances inside the reactor may be determined with high precision in the case of continuous process management, so that the passage times with respect to the biological decomposition may be optimized. In the solutions named at the outset, only a mean dwell time value could be determined due to the longitudinal and transversal mixing by means of the agitator.
The laden process air or the laden pressurized air, respectively, are supplied to a waste gas purification wherein organic constituents are separated and the purified air is recycled into the process.
The energy balance of the installation may be further improved if the laden leaching agent is supplied to a sewage water purification. The latter may contain a biogas installation wherein conversion of the organic matter into biogas takes place. Through energetic coupling of the liberated biogas, the process according to the invention may be designed to be largely self-sufficient as regards energy.
In the above described process management, the mixture of substances containing organic matter is subjected to a so-called hydrolysis wherein, through co-operation of air and leaching fluid, the organic material is dissolved and acidified as a result of aerobic, thermophilic heating by the air and carried off by the leaching fluid. I.e., decomposition of the organic constituents takes place as a result of setting a certain humidity and supplying clean air.
Further processing of the mixture of substances provides for drying of the residue in accordance with the invention. Such drying may be effected at minimum energetic expense by aerobic, thermophilic heating of the residue in the reactor. To this end, the mixture of substances may either be subjected to application of clean air in the reactor, so that by the resulting aerobic heating water vapor is discharged via the supplied air; and the residue is dried. Drying and hydrolysis in one single reactor is, however, under the condition of batch-type operation which should be viable only in smaller installations. In larger-sized installations a separate reactor (dryer) is provided for aerobic, thermophilic heating of the residue from hydrolysis. As a matter of fact, these two reactors may also be arranged behind each other in n-fold succession in a single container, so that several hydrolysis/drying steps may follow in succession.
The energy balance of the installation may be further improved if the laden leaching agent of a purification of sewage water is supplied. The latter may contain a biogas installation in which conversion of the organic matter into biogas takes place. Through energetic coupling of the liberated biogas, the process according to the invention may be designed to be self-sufficient as regards energy.
It is quite particularly advantageous if the solid fraction thus treated is supplied to a compacting step following hydrolysis and/or aerobic drying. Here the solid matter presenting a certain particle diameter is pressed into a predetermined geometrical shape, for example pellets or briquets. This compacting step results in further dewatering of the mixture of substances to be treated, so that following compacting a dry-stable body is present which cannot be eluted any further.
This body may, for example, be stored as a substitute fuel being an alternative for fossile energy carriers, or in a garbage dump.
The main application of the process according to the invention presumably resides in the treatment of waste matter; in principle the process may, however, also be applied for any other mixture of substances including organic constituents.
As a washing agent, water is customarily used which is recycled in the process of the invention. The air for hydrolysis and thermophilic drying of the mixture of substances may be guided in counterflow to the mixture of substances but also in parallel flow.